In general, as a measurement method for neutral fat, there are (1) a method using chromotropic acid, (2) an acetylacetone method, (3) an enzyme method, and (4) a method using a nephelometer, however, any of these methods requires complicated analysis operations and long analysis time. Therefore, a biosensor has been developed, as a method for determining, simply and quickly, quantity of objective substances without execution of dilution or stirring of a sample liquid, in measurement of specific components contained in the sample.
As such a biosensor for measurement of neutral fat, there is a triglyceride sensor characterized in that a glycerol ester hydrolase is immobilized onto a porous polymer membrane or a hydrophilic uniform polymer membrane covered onto a gate insulating film of a pH sensitive, ion selective electric field effect transistor (JP-A-59-210356).
In addition, a neutral fat sensor using a lipoprotein lipase and a glycerol oxidase is also known (JP-A-59-228158). This sensor is one having a first electrode and a second electrode, and arranged with an immobilized enzyme at the vicinity of one electrode, so as to measure neutral fat contained in a solution to be measured, based on current flowing between membrane electrodes, and a lipoprotein lipase and a glycerol oxidase are used as the immobilized enzyme. However, this apparatus is complicated, because it is composed of a glass inner tube and a glass outer tube, and provided with a first electrode at the bottom of the inner tube; inner liquid is charged between the inner tube and the outer tube; and a second electrode is arranged in this inner liquid, which electrodes are immersed in a water tank maintained at 30° C., and a sample to be measured is charged in this water tank.
As a simpler and more convenient apparatus, a sensor for measuring substrate concentration of a sample liquid, by detecting electrochemically substance concentration change in a reaction among an enzyme, an electron mediator and a sample liquid by way of an electrode system, which has at least a measurement electrode and a counter electrode formed onto an insulating substrate, has been proposed (JP-A-2001-343349). This sensor is a sensor for measurement of neutral fat, which has a first layer formed onto a measurement electrode, by retaining a lipoprotein lipase, a glycerol kinase, a glycerophosphate oxidase and a surfactant, and by mounting a carrier through which a sample liquid can pass; and has a second layer formed onto a counter electrode, by retaining a surfactant, and by mounting a carrier through which a sample liquid can pass.